An investigation on the most suitable size of curved pits and the best plantation place inside the curves (Case study: Koomiran rangelands, Ghaen, southern Khorassan)

Curved pits have been constructed in the upper slopes of Mohammadabad-e-Chahak playa, in order to reduce runoff entrance and thereby control the playa extension. Seeds of Haloxylon persicum and Atriplex canescence have also been sown inside the pits. This research was aimed to investigate effects of pit size and pit zones on establishment rates of the cultivated or naturally growing plants. Along the line transects, 30 pits were created within the streams and 30 in flat areas. A hypothetical pit was also considered close to each pit, with the same dimensions. The number of cultivated and naturally growing plants was counted in five different zones within each pit. Plant establishment was higher for the pits created inside the streams as compared to the flat areas. The number of established A. canescence and naturally growing plants was increased by increasing the size of curved pits, however it did not affect the establishment of H. persicum seedlings. The cultivated plants showed the highest establishment in the middle of the ridge; but the highest number of naturally growing plant was found in the center of pits. The percentage of pit destruction was increased by increasing their size, nevertheless the number of broken pits was low (15%). Accordingly, we suggest, creating pits inside the streams, rather than flat areas, small pits (6-8 m2) for H. persicum but large pits (10-12 m2) for A. canescence.